RESUMO
Some characteristics of uptake of [8-(14)C]N(6)-benzyladenine (BA) by watermelon (Citrullus vulgaris Schrad., cv. Fairfax) cotyledons that were either excised immediately after 24 hours inhibition (day 0) or cultured in the dark for 48 hours on moist filter paper (day 2) have been compared.The uptake of BA seems to be passive in cotyledons of both kinds. The initial rate of uptake is, however, much slower in day 2 cotyledons. This is probably due to a higher resistance of cell membranes to BA influx. When the day 2 cotyledons are frozen and thawed, so that the membrane barrier is abolished, the amount of BA taken up is the same as in day 0 cotyledons.In spite of the lower rate of uptake, the physiological effects of BA in day 2 cotyledons are as strong as in day 0 cotyledons and occur with a shorter lag time. Sensitivity to BA seems indeed to start 24 to 48 hours after excision.
RESUMO
The uptake of 8-[(14)C]N(6)-benzyladenine (BA) was studied in excised watermelon (Citrullus vulgaris Schrad.) cotyledons 24 hours after the start of imbibition. The passive nature of this uptake is suggested by the following evidence: (a) no sign of saturation on increasing external concentration of BA; (b) no decrease in uptake under conditions that inhibit ATP synthesis; (c) no change in amount of radioactivity absorbed when cotyledons are frozen and thawed before the uptake test. About two-thirds of the radioactivity taken up is released after 12 hours of washing. If the washing is performed at 2 C very little radioactivity is released.There seems to be a correlation between the level of radioactivity (i.e. of BA + derivatives) present in the cotyledons and the magnitude of hormonal responses that are observed four days after uptake. This relationship holds regardless of whether a given level of radioactivity has been reached after a short period of uptake or after a long period of uptake followed by washing.
